FAQ: Report viewer zenon gives an error saying download report builder but it is already installed

Check the version of the installed Report Builder. There is a known bug that zenon is not compatible with Report Builder 15.1: 

Bug 301111: Report Viewer is not compatible with Report Builder 15.1

If Report Builder 15.1 is installed than uninstall it and install the Report Builder from the zenon setup iso.
"Setup\SetupPrerequisites\Microsoft Report Builder"

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